Interconnect structures and methods of making the same

ABSTRACT

The various embodiments of the present invention provide a stress-relieving, second-level interconnect structure that is low-cost and accommodates TCE mismatch between low-TCE packages and PCBs. The various embodiments of the interconnect structure are reworkable and can be scaled to pitches from about 1 millimeter (mm) to about 150 micrometers (μm). The interconnect structure comprises a dielectric body element and at least one interconnection array that provides a conductive path between two electronic components. Each interconnection array comprises a plurality of wires that provide both conductivity and compliance to the overall interconnect structure. The versatility and scalability of the interconnect structure of the present invention make it a desirable structure to utilize in current two-dimensional and ever-evolving three-dimensional IC structures.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/319,617, filed 31 Mar. 2010, which isincorporated herein by reference in its entirety as if fully set forthbelow.

BACKGROUND

1. Field

The various embodiments of the present invention relate to interconnectstructures, wherein features of the interconnect structure may bealtered to achieve desired fine-pitch and low-stress properties, and tomethods of making and using the same.

2. Description of Related Art

Interconnects facilitate electrical communication between variouselectronic components within an electronic system. A “first-level”interconnect, for example, facilitates electrical communication betweenintegrated circuits (“ICs”) and package leadframes. A “second-level”interconnect, for example, facilitates electrical communication betweenpackages and printed circuit boards (“PCBs”).

As the semiconductor industry migrates from two-dimensional ICs tothree-dimensional ICs, new second-level interconnect structures thatachieve higher electrical performance and successfully integrateheterogeneous ICs are needed. Specifically, new packaging techniquesthat are cost-effective, thermo-mechanically reliable, and providecompliant and reworkable second-level interconnections from large-body,low thermal coefficient of expansion (“TCE”) packages to PCBs at finepitches are desirable.

Two second-level interconnect structures are currently used. The firststructure is based on land grid array (“LGA”) packages, which areassembled onto a socket with flexible pins that contact lands on thepackage. These sockets are typically assembled onto a PCB with the helpof solders. The package is then plugged into the sockets, thereforemaking it removable and reworkable for processor upgrades. The secondstructure is a solder based assembly that does not require an underfill.

These interconnect structures, however, face fundamental challenges asthe trend towards three-dimensional ICs and silicon and glass-basedlow-TCE interposer packages with fine-pitch board level assembly gainsmomentum. First, providing a means for stress-relief within the currentinterconnect structures can be costly. Lower cost options, however, tendto induce tremendous TCE mismatch between low-TCE packages and PCBs.This mismatch subsequently creates fundamental limitations in scalingdown the pitch size with traditional solder compositions. Third, currentunderfill requirements prevent reworkability.

Alternative second-level interconnect structures are thus desirable thataddress these fundamental limitations and enhance thermo-mechanicalreliability without compromising cost, reworkability, or electricalperformance.

BRIEF SUMMARY

Various embodiments of the present invention provide an interconnectstructure, comprising a dielectric body element comprising a top surfaceand a bottom surface and at least one interconnection array comprising aplurality of conductive wires dispersed within the dielectric bodyelement. A first portion of each of the conductive wires extendssubstantially perpendicularly beyond the top surface of the dielectricbody element and a second portion of each of the conductive wiresextends substantially perpendicularly beyond the bottom surface of thedielectric body element. Each of the conductive wires is physically andelectrically isolated from each other at least within the dielectricbody element. Further, the first and second portions can be configuredto provide compliance upon application of physical stresses thereto.Additionally, each of the at least one interconnection arrays can beconfigured to establish a conductive path between two independentelectronic components.

In an embodiment, a fraction of the first and second portions cancomprise a coating configured to minimize or prevent surface wetting bya solder composition.

In other embodiments, a ratio of the first portion to the second portioncan be greater than or equal to about 1.

The dielectric body element can be a low stiffness polymer. Thedielectric body can also be a high stiffness polymer, polymer-glasscomposite, or a ceramic material.

An average cross-sectional dimension of each of the plurality ofconductive wires can be about 10 nanometers to about 50 micrometers.

In other embodiments, spacing between each of the at least oneinterconnection arrays can be about 5 to about 1000 micrometers.Further, spacing between each conductive wire within the interconnectionarray can be about 10 nanometers to about 50 micrometers.

Alternative embodiments provided a system of interconnected electronicdevices, the system comprising a first electronic component, a secondelectronic component, and an interconnect structure interposed betweenthe first and second electronic components. The interconnect structurecan comprise a dielectric body element comprising a top surface and abottom surface, at least one interconnection array comprising aplurality of conductive wires dispersed within the dielectric bodyelement. A first portion of each of the conductive wires extendssubstantially perpendicularly beyond the top surface of the dielectricbody element and a second portion of each of the conductive wiresextends substantially perpendicularly beyond the bottom surface of thedielectric body element.

Each of the conductive wires are physically and electrically isolatedfrom each other at least within the dielectric body element. Further,the first and second portions can be configured to provide complianceupon application of physical stresses thereto. Additionally, each of theat least one interconnection arrays can be configured to establish aconductive path between two independent electronic components.

The interconnect structure can be a second-level interconnect structure.Further, a fraction of the first portion and the second portion arecoated.

Other embodiments provide a method of manufacturing an interconnectstructure, the method comprising providing a dielectric body elementcomprising a top surface, bottom surface, and at least oneinterconnection array comprising a plurality of conductive wires, andremoving a portion of the top surface and the bottom surface of thedielectric body element, such that a first portion and second portion ofeach of the conductive wires extends substantially perpendicularlybeyond the top surface and the bottom surface, respectively, of thedielectric body element. Each of the conductive wires is physically andelectrically isolated from each other at least within the dielectricbody element. The first and second portions can be configured to providecompliance upon application of physical stresses thereto. Each of the atleast one interconnection arrays can be configured to establish aconductive path between two independent electronic components.

The method can further comprise coating at least a fraction of the firstand second portions of each of the conductive wires to minimize orprevent surface wetting by a solder composition.

Alternative embodiments provide a method of manufacturing aninterconnect structure, the method comprising forming a plurality ofchannels within a dielectric body element, forming a conductive wirewithin each channel of the plurality of channels, and removing at leasta portion of a first surface and at least a portion of a second surfaceof the dielectric body element to expose portions of the conductivewires from the dielectric body element.

The method can further comprise patterning a photoresist on a firstsurface of the dielectric body element and removing the photoresist fromthe first surface of the dielectric body element.

Forming the plurality of channels can comprise anodization, plasmaetching, laser drilling, lithographic techniques using photosensitivepolymers, and/or molding a polymer over a wire template and subsequentlyreleasing the polymer.

Forming the conductive wire within each channel can compriseelectrolytic plating and/or electroless plating.

Removing the at least the portion of the first surface and the at leastthe portion of the second surface of the dielectric body element cancomprise etching the at least the portion of the first and secondsurfaces.

Removing the at least the portion of the first surface and the at leastthe portion of the second surface of the dielectric body element cancomprise chemical dissolution of the at least the portion of the firstand second surfaces.

The method can further comprise coating a fraction of the exposedportion of the conductive wires to minimize or prevent surface wettingby a solder composition. Coating the fraction of the exposed portion cancomprise selective removal of the dielectric body element such that aportion of the dielectric body element is the coating.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a second-level interconnect structure interposedbetween two electrical components, in accordance with exemplaryembodiments of the present invention.

FIGS. 2 a-b illustrate SMT-compatible, second-level interconnectstructures, in accordance with exemplary embodiments of the presentinvention.

FIG. 3 illustrates a nano stress-relief socket (“NSS”), second-levelinterconnect structure, in accordance with exemplary embodiments of thepresent invention.

FIG. 4 illustrates a method of making the various embodiments ofsecond-level interconnect structure, in accordance with exemplaryembodiments of the present invention.

FIG. 5 illustrates an NSS, second-level interconnect structure, inaccordance with exemplary embodiments of the present invention.

FIG. 6 illustrates deformation of an NSS, second-level interconnectstructure, in accordance with exemplary embodiments of the presentinvention.

FIG. 7 illustrates plastic strain of an NSS, second level interconnectstructure, in accordance with exemplary embodiments of the presentinvention.

FIG. 8 illustrates stress components and warpage of an NSS, second-levelinterconnect structure, in accordance with exemplary embodiments of thepresent invention.

FIGS. 9-13 illustrate strain results of NSS, second-level interconnectstructures, in accordance with exemplary embodiments of the presentinvention.

FIG. 14 illustrates a substrate design, in accordance with exemplaryembodiments of the present invention.

FIGS. 15-18 illustrate various pad designs, in accordance with exemplaryembodiments of the present invention.

FIG. 19 illustrates a dielectric body element and interconnection arrayshaving too short of an exposure time, in accordance with exemplaryembodiments of the present invention.

FIG. 20 illustrates a dielectric body element and interconnection arrayshaving too long of an exposure time, in accordance with exemplaryembodiments of the present invention.

FIG. 21 illustrates laser drilled channels, in accordance with exemplaryembodiments of the present invention.

FIG. 22 illustrates laser drilled channels after O₂ plasma etching, inaccordance with exemplary embodiments of the present invention.

FIGS. 23-25 graphically illustrate plasma etching results, in accordancewith exemplary embodiments of the present invention.

FIG. 26 graphically illustrates laser ablation results, in accordancewith exemplary embodiments of the present invention.

FIGS. 27-28 illustrate various interconnect structures, in accordancewith exemplary embodiments of the present invention.

FIG. 29 graphically illustrates performance of an interconnectstructure, in accordance with exemplary embodiments of the presentinvention.

FIGS. 30-32 illustrate various methods of making nanochannels, inaccordance with exemplary embodiments of the present invention.

FIG. 33 illustrates a side view of an interconnect structure, inaccordance with exemplary embodiments of the present invention.

DETAILED DESCRIPTION

Referring now to the figures, wherein like reference numerals representlike parts throughout the several views, exemplary embodiments of thepresent invention will be described in detail. Throughout thisdescription, various components can be identified as having specificvalues or parameters, however, these items are provided as exemplaryembodiments. Indeed, the exemplary embodiments do not limit the variousaspects and concepts of the present invention as many comparableparameters, sizes, ranges, and/or values can be implemented.

It should also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an,” and “the” include pluralreferences unless the context clearly dictates otherwise. For example,reference to a component is intended also to include composition of aplurality of components. References to a composition containing “a”constituent is intended to include other constituents in addition to theone named. Also, in describing the preferred embodiments, terminologywill be resorted to for the sake of clarity. It is intended that eachterm contemplates its broadest meaning as understood by those skilled inthe art and includes all technical equivalents which operate in asimilar manner to accomplish a similar purpose.

Values may be expressed herein as “about” or “approximately” oneparticular value, this is meant to encompass the one particular valueand other values that are relatively close but not exactly equal to theone particular value. By “comprising” or “containing” or “including” ismeant that at least the named compound, element, particle, or methodstep is present in the composition or article or method, but does notexclude the presence of other compounds, materials, particles, methodsteps, even if the other such compounds, material, particles, methodsteps have the same function as what is named.

It is also to be understood that the mention of one or more method stepsdoes not preclude the presence of additional method steps or interveningmethod steps between those steps expressly identified. Similarly, it isalso to be understood that the mention of one or more components in acomposition does not preclude the presence of additional components thanthose expressly identified.

As used herein, the terms “interconnect” and “interconnect structure”may used interchangeably and refer to devices that can be used forconnecting electronic components across one or more of the generallyaccepted six levels of interconnection in an electronic system. Further,the term printed wiring board (“PWB”) and printed circuit boards(“PCBs”) may be used interchangeably.

The various embodiments of the present invention provide astress-relieving, second-level interconnect structure that is low-costand accommodates TCE mismatch between low-TCE packages and PCBs. Thevarious embodiments of the interconnect structure are reworkable and canbe scaled to pitches from about 1 millimeter (mm) to about 150micrometers (μm).

The stress-relief interconnect structure is surface mount technology(“SMT”) compatible and thus can be bonded to an interposer and can serveas a vertical interconnect that decouples the stresses and strainsbetween the bonded devices, packages, or boards. In other embodiments,the stress-relief interconnect structure can be used as a thin filmsocket, also known as a “nano stress-relief socket” (“NSS”), designed toplug-in a die or interposer on one side and assembled on a package orprinted wiring board (“PWB”) using solders on the other side.

The versatility and scalability of the interconnect structure of thepresent invention make it a desirable structure to utilize in currenttwo-dimensional and ever-evolving three-dimensional IC structures.

Referring to FIG. 1, exemplary embodiments of the interconnect structure115 comprise a dielectric body element 110, at least one interconnectionarray 115 dispersed within the dielectric body element 110, and aplurality of conductive wires 120 within the at least oneinterconnection array 115.

The dielectric body element 110 is formed from a nonconductive elementand thus electrically isolates two independent electrical components125/130 from each other. The dielectric body element 110 can be madefrom a polymeric material, and more specifically, can be made from alow-stiffness polymer, a high stiffness polymer, polymer-glasscomposite, or a ceramic material. In exemplary embodiment, the stiffnessvalues range from about 0.1 GPa to about 50 GPa. The polymers can besilicones, epoxies, fluoropolymers, siloxanes, reinforced prepregs, andothers. The dielectric body element 110 has a top surface and a bottomsurface, and in exemplary embodiments, the thickness of the dielectricbody element 110 (i.e., the distance between the top surface and thebottom surface) can be about 10 μm to about 50 μm. The thickness of thedielectric body element 110, however, is not limited to theseparameters.

At least one interconnection array 115 can be dispersed within thedielectric body element 110. In other exemplary embodiments, a pluralityof interconnection arrays 115 can be uniformly dispersed within thedielectric body element. Each interconnection array 115 is physicallyand electrically isolated from other interconnection arrays 115. Inexemplary embodiments, spacing between each of the interconnectionarrays 115 can be about 5 μm to about 1000 μm (1 mm), and the width ofthe interconnection arrays can be about 300 μm (0.3 mm). Eachinterconnection array 115 provides an isolated conductive path betweentwo electronic components 125/130. For example, embodiments thatcomprise two interconnection arrays 115 provide two separate conductivepaths between electronic components 125/130. Because the dielectric bodyelement 110 is nonconductive, the interconnection arrays 115 enableelectrical communication between the two electronic components. Theelectronic components 125/130 can be, for example, an integratedcircuit, an interposer, a substrate, a printed circuit board, a printedwiring board.

Each interconnection array 115 comprises a plurality of conductive wires120. In exemplary embodiment, each interconnect array 115 comprises tento thousands of conductive wires 120. One skilled in the art willunderstand that the term “wires” is synonymous with fibers and allderivatives thereof. The conductive wires 120 are configured such that afirst portion 135 of each of the conductive wires 120 extendssubstantially perpendicularly beyond the top surface of the dielectricbody element 110 and a second portion 140 of each of the conductivewires extends substantially perpendicularly beyond the bottom surface ofthe dielectric body element 110.

The conductive wires 120 are physically and electrically isolated fromeach other at least within the dielectric body element 110. However,upon an application of physical stress, the first portion 135 and secondportion 140 of the conductive wires 120 may slightly deform and comeinto physical and/or electrical contact outside of the dielectric bodyelement 110. The isolation of the conductive wires 120 within thedielectric body element 110 provides near-zero stress compliance to theinterconnection structure 105 when interposed between two electricalcomponents 125/130. Thus, one element, i.e., the conductive wires 120,is responsible for providing both conductivity and near-zero stresscompliance to the interconnect structure 105.

The conductive wires 120 can be formed from many conductive materialsand can be of many shapes and sizes. For example, the conductive wirescan be made from copper, carbon fiber, carbon/graphite fiber, dopedsilicon, conductive particle or ionic salt filled polymeric fibers,and/or metallized fibers. Other materials can include nickel, aluminum,or other metals or metallic alloys, conducting polymers, and conductingoxide fibers. Further, the cross-section of the conductive wires 120 canbe of many geometrical configurations. In exemplary embodiments, thecross-section of the conductive wires 120 are substantially circular andthe average cross-sectional dimension of the conductive wires 120 can beabout 10 nanometers (nm) to about 10 μm. The conductive wires can be,for example, nanowires, nanotubes, nanorods, microwires, microtubes,and/or microrods.

In exemplary embodiments, the length of the first portion 135 and thesecond portion 140 of the conductive wires 120 ranges from about 10 μmto about 80 μm. In one embodiment, the first portion 135 is longer thanthe length of the second portion 140. In another embodiment, the ratioof the first portion 135 to the second portion 140 is greater than orequal to about 1. This configuration enhances the overall compliance ofthe interconnect structure 120. Thus, one skilled in the art willunderstand that the lengths of the first portion relative to the secondportion can be manipulated to achieve desired compliance.

Further, one skilled in the art will understand that the parametersdescribed in reference to the dielectric body element 110, theinterconnection arrays 115, and the conductive wires 120 can bemanipulated to achieve a desired pitch size, therefore making theexemplary embodiments of the interconnect structure 105 desirable forthree-dimensional interposer applications. The interconnect structure105 can also be extended to other critical technologies, such aswafer-probing and hermetic feed-throughs for biocompatible packaging.

The various embodiments of the interconnect structure 105 are both SMTand NSS compliant. Referring to FIGS. 2 a and 2 b, there is shown anSMT-compliant interconnect structure 205. In this embodiment, theinterconnect structure 205 can be surface-mounted to an IC or interposer210 and serve as a vertical interconnect that decouples the stresses andstrains between the bonded devices, packages, or boards 215. Referringto FIG. 3, there is shown an NSS-compatible interconnect structure 305designed to “plug-in” a die or interposer 310 on one side and assembledon a package or PWB 315 on the other side.

In exemplary embodiments of the interconnect structure 105, theinterconnection arrays 115 can provide conductive paths between twoelectrical components 125/130 via solder connections disposed on theinterconnection-facing side of each of the electrical components. As theinterconnect structure 105 is interposed between two electricalcomponents 125/130, the conductive wires 120 of the interconnectionarrays 115 physically engage the solder compositions. The solder canthen “wick” or flow up and through the conductive wires 120. In mostembodiments, however, it is undesirable for the solder to completelysaturate the conductive wire 120 as over-saturation interferes with theoverall compliance of the interconnect structure 105. Thus, to limitsurface-wetting from the solder composition, a fraction of the firstportion 135 and second portion 140 of the conductive wires 120 can becoated. Coatings that can prevent solder wetting are made of conformalpolymers, oxides, nitrides, or non-wettable metals, such as titanium andnickel. These coatings can then be selectively removed from the tip ofthe fibers to allow wetting only on the top portion of the fibers. Thiscoating thus allows the solder composition to partially wick at the tipof the conductive wires 120, yet effectively prevents the soldercomposition from bonding to the side walls and penetrating the interiorportion of the conductive wires 120.

In other embodiments, the interconnection arrays 115 can provideconductive paths between two electrical components 125/130 using otherbonding methods such as conductive or non-conductive adhesives,mechanical interlocking, thermocompression, thermosonic, or diffusionbonding.

FIG. 4 provides an exemplary method for manufacturing the interconnectstructure 105. A low-stiffness, polymeric dielectric body element isfirst provided and a plurality of channels are formed therein 405. Theplurality of channels can be uniformly dispersed within the dielectricbody element and can extend from a first surface to a second surface ofthe dielectric body element. One skilled in the art will appreciate thatthe plurality of channels coincide with the interconnection arrays ofthe completed interconnect structure. The plurality of channels can befabricated through both top-down and bottom-up approaches, which reducesthe overall manufacturing cost and enables the interconnect structure tobe scaled to any pitch. The channels can be formed using varioustechniques, for example, anodization of metal foils to form porousnanochannel structures (some class of which are referred to as AnodizedAluminum Oxide templates—AAO), laser drilling, plasma etching, ionbombardment, nanoimprinting, and/or embossing techniques. Further, theplurality of channels can be defined within the dielectric body elementto be micro-sized, nano-sized, or a combination thereof.

The channels can be made in a pre-patterned way with a photoresist todefine the channels followed by plasma etching or laser ablation, orusing a CAD (computer aided design) controlled drilling process usinglaser or mechanical processes, or lithographic processes forphotosensitive dielectrics. The channels can also be made by formingreverse mold with metal or silicon needles, filling it with polymer, andthen remove the mold to form channels in-situ, as illustrated in FIG.30.

A photoresist can be subsequently added to the first surface of thedielectric body element 410 into a pattern compatible with theelectronic component being connected. A plurality of conductive wirescan then be placed in each of the plurality of channels 415. Theconductive wires can be placed within the plurality of channels usingvarious plating techniques, for example, electrolytic plating and/orelectroless plating. It is to be noted that electroless plating happensfrom the side-wall filling, as illustrated in FIG. 31, whileelectrolytic plating involves plating from bottom-up or side-wall orcombinations of both, as illustrated in FIG. 32. The photoresist canthen be removed from the first surface of the dielectric body element420. However, if the channels are formed in a pre-patterned way insidethe dielectric, the photoresist process can be avoided since plating isonly confined to the channels. The extra copper in the top and bottomcan be removed by etching it away. Examples of pre-fabricated channelscan be found in FIGS. 21-22.

Further, at least a portion of the first and second surfaces of thedielectric body element can be removed 425, such that the first andsecond portions of each of the conductive wires extend substantiallyperpendicularly beyond the top surface and bottom surfaces of thedielectric body element 425. The first and second surfaces of thedielectric body element can be removed by laser ablation, plasma etchingand/or chemical dissolution techniques. The complete interconnectstructure can then be interposed between two electrical components, suchthat the conductive wires contact solder compositions from eachelectrical component, thus enabling the interconnection arrays toprovide conductive paths between electrical components. If desired, afraction of the exposed conductive wires can be coated to limit surfacewetting from the solder compositions.

The coatings can simply be formed by selective removal of the first andsecond surfaces of the dielectric body elements using lithographicmethods such that a coating of the dielectric body element is leftbehind, around each individual conductive wire.

The coatings to prevent surface wetting can also be formed by firstcoating the wires with a metal, such as palladium, second coating thewires with a metal, such as copper, and selectively removing the metalsfrom the tip. The coatings can also be formed by monolayer or multilayerchemisorptions techniques, spray, spin, dip and other wet coatingtechniques and other electroless metallization techniques, and/orchemical vapor deposition or physical vapor deposition techniques ofoxides, nitrides, polymers. The coating can be selectively removed withanistropic etching.

EXAMPLES

The various embodiments of the present invention are illustrated by thefollowing non-limiting example.

Example 1 Two-Dimensional NSS Models

Two-dimensional, half symmetric models in which a package is connectedto a printed wiring board by NSS approach were built to study thereliability of the NSS interconnection. Linear plane stress elementswith quadrilateral shape were used for the simulation. The influences ofmultiple geometry and material parameters on the reliability ofinterconnection were studied, including copper wire length, copper wirediameter, copper wire spacing, polymer thickness and package material.

The geometry of the NSS structure is illustrated in FIG. 5. Copper wireswith about 2 μm diameter and about 4 μm pitch were inserted in thepolymer dielectric layer and connect top solder and bottom solder. Thepackage material used in this model was silicon, with a thickness ofabout 1 millimeter (mm). The printed wiring board was made of FR-4, witha thickness of 1 mm. Pitch (the width of each unit) was about 1 mm, andthe width of the whole structure was about 30 mm.

The solder material (SnAgCu) has temperature dependent elastic plasticproperties, as shown in Table 1, all other materials were modeled aselastic materials, listed in Table 2.

Symmetric boundary conditions are applied at the structure, where thedisplacements in x direction of the nodes on the inner boundary are setto be zero, and the origin point is pinned.

TABLE 1 Temperature (° C.) Young's Modulus (MPa) Yield Stress (MPa) −2555790 41.645 25 52620 31.835 75 49290 20.975 125 45830 13.635

TABLE 2 Young's Thermal Expansion Modulus Coefficient Poisson's Material(MPa) (ppm/° C.) Ratio Silicon (package) 130000 2.70 0.28 RXP-4M(polymer layer) 1345 45 0.3 Copper (copper wire) 104000 17 0.33 FR4(PWB) 24000 16 0.15

A static simulation of the cooling down process from reflow temperature(about 260° C.) to room temperature (about 25° C.) was performed. Sinceno time-dependent properties are used for materials, the cooling rate isnot specified in simulation.

Shear strain was generated in solders during the cooling down process,due to the difference in expansion (shrinkage) ratio of the package andprinted wiring board. In NSS structures, considerable deformation isundertaken by the compliant copper wires, as shown in FIG. 6.

The equivalent plastic strains accumulated in the solders during thecooling down process were collected as the critical parameter toestimate reliability of the interconnection. The maximum plastic strainhappens at the furthest solder, since it has the largest distance toneutral point (DNP). The maximum plastic strain was about 0.003, shownin FIG. 7. Stress components and warpage are illustrated in FIG. 8. Themaximum axial stress and peel stress are about 35 MPa, maximum shearstress is about 19 MPa, and warpage is about 0.17 mm.

A parametric study was performed to illustrate the influence of multiplegeometry and material parameters. A model with coarse copper wires wasfirst built as a control of the study, illustrated in FIG. 9. Largeplastic strain (about 1.263) was observed in solders.

NSS structure with longer copper wires were shown to be more reliable. Amodel with about 37.5 μm free copper wire both on top and bottom ofabout 25 μm thick polymer layer connecting package and PWB was alsobuilt. And the equivalent plastic strain was decreased by about 34%, asshown in FIG. 10.

More copper wires in each unit (less spacing between copper wires) canincorporate more deformation during the cooling down process. In themodel where there were 10 wires in each unit (compared to 5 in previousmodel), the plastic strain decrease by about 70.7%, as shown in FIG. 11.

To obtain better estimation of the reliability of NSS interconnection inreal assembly, a model with fine pitch was built. As shown in FIG. 12,the interconnect pitch was about 300 μm, and the package size was aroundabout 28.3 mm, with 95 units tied together. The maximum plastic strainwas shown to be about 0.1132.

Organic materials are the mainstream materials used in package. A modelwhere silicon substrate is replaced by a 0.4 mm BT substrate was built.Imbalanced copper wires (longer free length on top than on bottom) canincorporate more deformation, shown as in FIG. 13. The maximum plasticstrain was around 3%.

Example 2 Pad Designs and Fabricated Structures

In this example, four different pad designs were tested. The substratedesign for the examples described herein is illustrated in FIG. 14. Thepads were arranged in 10×10 mm coupons, wherein there were 16 couponsfor each design. One skilled in the art will understand that the paddesign is indicative of the configuration of the interconnection arraysand the conductive wires incorporated therein.

The first pad design, illustrated in FIG. 15, had a pitch of about 500μm, a wire diameter of about 50 μm, and a distance between wires ofabout 50 μm. The second pad design, illustrated in FIG. 16, had a pitchof about 500 μm, a wire diameter of about 75 μm, and a distance betweenwires of about 25 μm. The third pad design, illustrated in FIG. 17, hada pitch of about 300 μm, a wire diameter of about 50 μm, and a distancebetween wires of about 25 μm. The fourth pad design, illustrated in FIG.18, had a pitch of about 300 μm, a wire diameter of about 25 μm, and adistance between wires of about 25 μm.

The dielectric body element was then further developed. The dielectricbody was formed by laser drilling, plasma etching, and laser ablationtechniques. In some embodiments, the laser drilling technique includedthe removal of copper from one side prior to drilling. The plasmaetching and laser ablation technique included thinning down copper onone side to less than about 5 μm, laminating with photoresist FX920 (20μm thickness), exposing for about 15 to 20 seconds with 20 mW/cm², anddeveloping and etching the copper. It was found that smaller structureshad better performance with less exposure time, and larger structureshad better performance with more exposure time. Further, it was foundthat temperature and etch time are important parameters for plasmaetching. Similarly, the channels for the interconnection arrays wereformed by laser drilling, plasma etching, and laser ablation techniques.

FIG. 19 illustrates a dielectric body element and interconnection arrayshaving too short of an exposure time. FIG. 20 illustrates a dielectricbody element and interconnection arrays having too long of an exposuretime. FIG. 21 illustrates laser drilled channels and FIG. 22 illustrateslaser drilled channels after O₂ plasma etching. In this example, it wasfound that the laser drilled substrate had to be cleaned with the O₂plasma for about 10 minutes to clean the borders of the holes. FIGS. 23to 25 provide graphically illustrate plasma etching results for variousembodiments of the present invention.

In reference to plasma etching, it was found that UL 3850 HT etches fartoo slow to drill thru 100 μm material, and that isotropic etching willalso cause a much wider opening than is needed. Parameters that affectthe etch rate are (1) the kind of material that is used: UL 3850, HT 0.5μm/h was used; (2) the position in plasma chamber: the higher the shelfthe higher the etch rate; (3) pressure: occasionally the pressuredropped below the set point and 50 μm of substrate were removed within a3 h session; (4) amount of material in the chamber: it is recommended touse a FR4 board as carrier to ensure evenly etching of the substrate butthe etch rate will drastically increase by just putting the substrateitself in the chamber.

Various laser ablation techniques were also tested including UV, CO₂ andexcimer. FIG. 26 illustrates contact profilometry results for etch-depthafter 500 excimer laser pulses on R/FLEX 3850.

Testing with UL 3850 HT revealed a low etch rate which was due to carbonredeposition during laser ablation. Intermediate O₂ plasma cleaningsteps were introduced with cycle time of 10-20 minutes.

FIGS. 27, 28, and 33 show the successful production of 25 μm diameter,released copper wires in UL 3850 HT material. The holes were laserdrilled thru the laminated copper on both sides. Later the holes on thebackside were closed by electro plating additional copper. The next stepinvolved removal of all copper on the front side by using micro etchsolution. Electro plating was then used again to bottom up fill theholes an produce the wires, which then were released using the plasmaetch chamber. FIG. 29 shows a complete released 25 diameter wirestructure.

While the present disclosure has been described in connection with aplurality of exemplary aspects, as illustrated in the various figuresand discussed above, it is understood that other similar aspects can beused or modifications and additions can be made to the described aspectsfor performing the same function of the present disclosure withoutdeviating therefrom. For example, in various aspects of the disclosure,methods and compositions were described according to aspects of thepresently disclosed subject matter. However, other equivalent methods orcomposition to these described aspects are also contemplated by theteachings herein. Therefore, the present disclosure should not belimited to any single aspect, but rather construed in breadth and scopein accordance with the appended claims

We claim:
 1. An interconnect structure, comprising: a dielectric bodyelement comprising a top surface and a bottom surface; at least oneinterconnection array comprising a plurality of conductive wiresdispersed within the dielectric body element; wherein a first portion ofeach of the conductive wires extends substantially perpendicularlybeyond the top surface of the dielectric body element and a secondportion of each of the conductive wires extends substantiallyperpendicularly beyond the bottom surface of the dielectric bodyelement; wherein each of the conductive wires are physically andelectrically isolated from each other at least within the dielectricbody element; wherein the first and second portions are configured toprovide compliance upon application of physical stresses thereto; andwherein each of the at least one interconnection arrays is configured toestablish a conductive path between two independent electroniccomponents with an array of pads, wherein the conductive path betweenthe pads comprises a plurality of wires that are periodically patternedas a parallel wide array.
 2. The interconnect structure of claim 1,wherein a fraction of the first and second portions comprises a coatingconfigured to minimize or prevent surface wetting by a soldercomposition.
 3. The interconnect structure of claim 1, wherein a ratioof the first portion to the second portion is greater than or equal toabout
 1. 4. The interconnect structure of claim 1, wherein thedielectric body element is a low stiffness polymer.
 5. The interconnectstructure of claim 1, wherein the dielectric body is a high stiffnesspolymer, polymer-glass composite, or a ceramic material.
 6. Theinterconnect structure of claim 1, wherein an average cross-sectionaldimension of each of the plurality of conductive wires is about 10nanometers to about 50 micrometers.
 7. The interconnect structure ofclaim 1, wherein a spacing between each of the at least oneinterconnection arrays is about 5 to about 1000 micrometers.
 8. Theinterconnect structure of claim 1, wherein a spacing between eachconductive wire within an interconnection array is about 10 nanometersto about 50 micrometers.
 9. A system of interconnected electronicdevices, the system comprising: a first electronic component with afirst set of pads; a second electronic component with a second set ofpads; and an interconnect structure interposed between the first andsecond electronic components, wherein the interconnect structurecomprises: a dielectric body element comprising atop surface and abottom surface; at least one interconnection array comprising aplurality of conductive wires dispersed within the dielectric bodyelement; wherein a first portion of each of the conductive wires extendssubstantially perpendicularly beyond the top surface of the dielectricbody element and a second portion of each of the conductive wiresextends substantially perpendicularly beyond the bottom surface of thedielectric body element; wherein each of the conductive wires arephysically and electrically isolated from each other at least within thedielectric body element; wherein the first and second portions areconfigured to provide compliance upon application of physical stressesthereto; and wherein each of the at least one interconnection arrays isconfigured to establish a conductive path between two independentelectronic components, wherein a conductive path between the first setof pads and the second set of pads is formed a plurality of conductingwires that are periodically patterned as a parallel wide array.
 10. Thesystem of claim 9, wherein the interconnect structure is a second-levelinterconnect structure.
 11. The system of claim 9, wherein a fraction ofthe first portion and the second portion are coated.